Optical scanner is widely used computer peripheral device which uses a light source module to provide light source to scan a document and uses a chassis to reflect document image to a charged couple device for converting the image to digital signals for computer process.
FIG. 1 illustrates a conventional scanner 1 which includes a document, board 2, a chassis 3, a transmission means 4 and a charged couple device (CCD) 5
The document board 2 is a rectangular and transparent member for holding a scanning document 6 thereon. The chassis 3 is located below the document board 2 and includes a plurality of reflection mirrors 31, a lens 32 and a light source module 7 for emitting light ray to the document 6. Image on the document 6 then is reflected to the reflection mirrors 31 and lens 32 which forms an image on the CCD 5 for converting to digital signals. The transmission means 4 drives the chassis 3 and CCD 5 moving reciprocally below the document board 2 to perform scanning operation.
FIG. 2 shows the light source module 7 used in the conventional scanner. It is engaged with the chassis 3 and moved synchronously with the chassis 3. The light source module 7 includes a lamp socket 71 and a lamp tube 72. The lamp socket 71 is a trough member having a length approximately same as the chassis 3 with an elongate opening 73 pointing toward the document board 2. The lamp tube 71 is nested in the trough and being held at two ends (not shown in the figure). The trough has circular crosssection and has a reflective sheet 74 or material covering the internal surface. Light ray from the lamp tube 72 may emit directly to the document board 2 through the opening 73 and may also reflect from the reflective sheet 74 and project to the document board 2 to augment light luminosity on the document board 2.
FIG. 3A illustrates relationship between luminosity and distance of the lamp tube 72. The lamp tube 72 may be considered as aggregation of many individual light spots. The middle portion of the lamp tube 72 has overlap light ray from the adjacent light spots and may result in greater luminosity. The two ends of the lamp tube 72 has less overlap light ray and will result in less luminosity. As a result, the photo electricity conversion in the CCD also will be affected. As shown in FIG. 3B, the middle portion of the CCD receives grater light intensity and will result in higher voltage while the two ends of the CCD will receive less light intensity and result in lower voltage. This phenomenon has greater impact on scanning quality. In order to remedy such problem, conventional approach is to coat or adhere a non-reflective material 75 on the reflective sheet 74. The non-reflective material 75 is taper off at two ends so that the two ends will have greater reflective surface to compensate the smaller light emitting intensity of the lamp tube at two ends to get an evenly distributed luminosity and voltage (as shown in FIGS. 4C and 4D). The non-reflective material 75 may be one piece (as shown in FIG. 4A) or two pieces (as shown in FIG. 4B).
However the conventional technique set forth above still has drawbacks, notably:
a. the trough for nesting the lamp tube is generally a circle or square in crosssection. It prones to produce random or mixed light emission and may result in poorer scanning quality. PA1 b. The non-reflective material is either printed or glued on the reflective sheet. The printing method will create environmental pollution problem. The gluing method is a tedious process and costs higher.
All of these concerns have yet to be resolved.